1. Field of The Disclosure
This disclosure relates to a liquid crystal display device, and more particularly, to a connection structure between a flexible cable and a light-emitting diode (LED) assembly functioning as a light source in a liquid crystal display device.
2. Discussion of The Related Art
Liquid crystal display (LCD) devices are widely used as monitors of notebook computers, monitors of personal computers and televisions due to excellent reproduction of moving images and high contrast ratio. LCD devices use the optical anisotropy and polarization properties of liquid crystal molecules of a liquid crystal layer to produce an image.
An LCD device includes two substrates spaced apart from each other and facing each other as well as a liquid crystal layer interposed between the two substrates. The alignment direction of the liquid crystal molecules is controlled by varying the intensity of an electric field applied to the liquid crystal layer, and changing the transmittance of light through the liquid crystal layer.
The LCD devices require an additional light source because the LCD devices are not self-luminescent. Therefore, a backlight unit is disposed at a rear side of a liquid crystal (LC) panel and emits light into the LC panel to display images. Figure (FIG. 1 is a cross-sectional view of a conventional liquid crystal display (LCD) device including LEDs as a light source. The LCD device of FIG. 1 includes a liquid crystal panel 10, a backlight unit 20, a support frame 30, a top cover 40 and a bottom cover 50. The liquid crystal panel 10 displays images and includes first and second substrates 12 and 14 facing and attached to each other with a liquid crystal layer (not shown) placed therebetween.
The backlight unit 20 is disposed at a rear side of the liquid crystal panel 10. The backlight unit 20 includes a light source, a reflection plate 25, a light guide plate 23 and a plurality of optical sheets 21. The light source is disposed at an edge of at least one side of the support frame 30 along a length direction. The reflection plate 25 is disposed over the bottom cover 50 and is colored in white or silver. The light guide plate 23 is disposed over the reflection plate 25. The plurality of optical sheets 21 are disposed over the light guide plate 23.
Edges of the liquid crystal panel 10 and the backlight unit 20 are surrounded by the support frame 30 having a rectangular shape. The top cover 40 covers edges of the front surface of the liquid crystal panel 10, and the bottom cover 50 covers a rear surface of the backlight unit 20. The top cover 40 and the bottom cover 50 are combined with the support frame 30 to thereby constitute a single body.
Unexplained reference numbers 19a and 19b indicate polarizers that are attached at front and rear surfaces of the liquid crystal panel 10 and control the polarization of light. The backlight unit 20 may include a cold cathode fluorescent lamp (CCFL), an external electrode fluorescent lamp (EEFL), and a light emitting diode (LED) as a light source. Among these light sources, the LED has been widely used due to its small size, low power consumption, and high reliability. In FIG. 1, LEDs 29a are mounted on an LED printed circuit board (PCB) 29b to form an LED assembly 29. The LED assembly 29 may be fixed by an adhesive such that light emitted from the LEDs 29a faces a side surface of the light guide plate 23 on which the light is projected. Therefore, light emitted from the LEDs 29a is projected on the side surface of the light guide plate 23 and then is refracted toward the liquid crystal panel 10 inside the light guide plate 23. With light reflected by the reflection plate 25, the light is changed to have uniform brightness and high qualities while passing through the plurality of optical sheets 21 and is provided to the liquid crystal panel 10.
An LED driving circuit (not shown) provides the LEDs 29a with driving voltages and controls on or off of the LEDs 29a. The LED driving circuit is disposed close to a rear surface of the bottom cover 50 to minimize a total size of the LCD device.
To electrically connect the LEDs 29a the LED driving circuit, a flexible cable (not shown) such as a flexible printed circuit (FPC) is disposed at a side of the LED PCB 29b to bend and connect the LED PCB 29b to the LED driving circuit on the rear surface of the bottom cover 50. The LED PCB 29b and the flexible cable are electrically connected to each other by soldering.
However, the backlight unit 20 having the above-mentioned structure has several problems. First, connection between the flexible cable and the LED PCB 29b is fragile. When the flexible cable is bent for connection to the LED driving circuit (on the rear surface of the bottom cover 50), disconnections of the flexible cable frequently occur, especially when an outer force is applied to a soldering area for connecting the flexible cable and the LED PCB 29b. This may cause malfunction of the LEDs 29a or damage to driving parts. In addition, there may be soldering problems such as cold solder or insufficient solder between the LED PCB 29b and the flexible cable, which may also cause malfunction of the LEDs 29a or damage the driving parts. Accordingly, the reliability of the LCD device is lowered due to weak connection of the flexible cable and the LED PCB 29b. 